1. Field of the Invention
The present invention relates to an advancing/retracting mechanism incorporated in a photographing (imaging) lens (lens barrel).
2. Description of the Related Art
An advancing/retracting mechanism for advancing or retracting a linearly guided movable member (linearly movable member) by a rotation of a cam ring is often used in a lens barrel and the like. In such an advancing/retracting mechanism which is incorporated in a photographing lens barrel, the maximum amount of movement of the linearly guided movable member along the photographing optical axis has been required to be great due to a growing trend in recent years to increase a variable-power ratio of a zoom lens. A simple way to increase the maximum amount of movement of the linearly guided movable member along the photographing optical axis is to increase the cam ring and a linear guide member in size, specifically the lengths of these elements in the optical axis direction. However, this increases the size of the photographing lens, which is not desirable, especially for compact cameras, which are required to be designed as small as possible to satisfy the current trend towards further miniaturization. The linear guide member which guides the movable member linearly without rotating the movable member is generally coupled to the cam ring to be immovable relative to the cam ring along the rotational axis thereof while allowing the cam ring to rotate relative to the movable member. Due to this structure, the size of the linear guide member (especially the length thereof) is limited by the cam ring. Accordingly, if the maximum amount of movement of the movable member is relatively great compared to the size of the cam ring, the movable member is difficult to be guided linearly without rotating with reliability over the entire range of movement of the movable member.